Summary: In the mid-1980s we carried out a prospective study of early pregnancy in which we enrolled 221 healthy women who were planning to become pregnant. These women collected daily urine specimens for up to six months. We've assayed these specimens to describe the hormonal events of the menstrual cycle and early pregnancy. 155 women became clinically pregnant during the study, while 44 had pregnancies that ended so early that the pregnancies were detectable only by assay of urinary human chorionic gonadotropin. This unique study has been called a landmark, and continues to provide a rich resource for the description of the earliest stages of pregnancy. (More than 30,000 urine samples are still being stored.) We've published more than 40 papers from this study over the past two decades, some of which have led to fundamental new understanding of conception and early pregnancy loss. Last year's progress. CORPUS LUTEUM RESCUE. One of the crucial events of early human pregnancy is the implantation of the blastocyst and its production of hCG, which sustains the function of the corpus luteum (CL). Without this "rescue," the CL quickly atrophies and triggers the onset of menses (and loss of any pregnancy that may have occured). Despite the importance of CL rescue, little is known about it in humans. Studies of non-human primates have shown an abrupt response of the CL as part of rescue, while the few data from humans suggest a more muted CL response. We analyzed daily hormone data from 136 successful human pregnancies to describe CL rescue. We found that CL rescue is indeed abrupt in humans, but it occurs at variable times following implantation. While CL rescue in humans appears to be fundamentally similar to the CL of non-human primates, our data also suggest the possibility of yet-undiscovered hormones supporting rescue of the CL in humans.